Multi-level wiring in integrated circuits is well known in the industry. In the early days of the semiconductor industry, nearly all of the resistance and the capacitive load in a circuit were in devices. As devices have grown smaller and the wiring cross-sections have been reduced, the capacitive load of the wiring structure and the line resistivity have grown to the point that they are the largest contributors to the total capacitive-resistance load on a device. Today, a major problem in the semiconductor processing industry is the capacitive-resistance effect in the wiring levels. Efforts to reduce the resistance of the wiring levels and to lower the capacitive loading on the wiring levels have met with poor results.
Conventionally, aluminum and aluminum alloys have been used for wiring integrated circuits. Aluminum, however, has a poor conductivity compared with other metals. Copper has also been used. However, copper, unlike aluminum, cannot be reactively ion etched. To be reactively ion etched, the object being etched must form a volatile compound at room temperature, and copper does not do so. Thus, wires, or lines, of copper must be formed in a damascene process. In the damascene process, a layer of insulating material is first deposited and patterned by reactive ion etching to form trenches. The conductor material, here copper, is deposited above a liner and adhesion layer within the trenches. Generally, the copper is deposited by either chemical vapor deposition (CVD) or electroplating. Any unwanted copper and liner may be removed by chemical mechanical polishing (CMP).
As lithographic dimensions decrease, the capacitive-resistance problem is increasing. The capacitive-resistance problem is affected by wires located in the same horizontal plane as well as by wires vertically separated. The capacitive effect of wires within the same plane is most directly affected by smaller lithographic dimensions. The horizontal and vertical capacitive effects can be mitigated to some extent by making the wiring thinner. Thinning the wiring, however, reduces the cross-section of the wiring, thereby increasing its resistance. Further, the vertical capacitive effect can be mitigated by increasing the thickness of the insulative material in which the various wiring layers are deposited. The insulative materials generally used have a low coefficient of thermal conductivity, thereby reducing the heat flow to the top surface of the integrated circuit, causing the integrated circuit to operate at a higher than desired temperature or a reduced power level to avoid an overheating problem.
Another solution to heat generation and dissipation is to make the wiring wider to increase the conductivity and/or electromigration resistance of the wiring. This, however, requires additional wiring planes, which consequently requires additional levels of insulative material, thereby reducing the ability to remove heat from the integrated circuit.
FIGS. 1–6 are exemplary depictions of conventional multiple level wiring layouts which have been used in integrated circuit designs. FIGS. 1–6 show a portion of an integrated circuit have wiring channels running in a first direction at a first level interspersed with wiring channels at a second level running in a second direction perpendicular to the first direction. With specific reference to FIGS. 1–2, an integrated circuit portion 10, which includes a substrate 13, is shown having a top surface 12, a bottom surface 14, a first side surface 16, a second side surface 18, a third side surface 20, and a fourth side surface 22. A first plane of wiring 30 and a third plane of wiring 34 extend from the first side surface 16 to the third side surface 20. A second plane of wiring 32 and a fourth plane of wiring 36 extend from the second side surface 18 to the fourth side surface 22. Each of the wiring planes 30, 32, 34, 36 includes one or more wiring channels 38 into which are deposited conductive wires 40. The wires may be formed of any conductive material, and are preferably formed of copper.
Each of the wiring planes 30, 32, 34, 36 is set within and separated by an insulator material, such as an intralayer dielectric 42. As shown, the second plane of wiring 32 is positioned between the first and third planes of wiring 30, 34, while the fourth plane of wiring 36 is beneath the third plane of wiring 34. The width of each of the wiring channels 38 is generally equivalent to the height of the channels 38, and the pitch is, for example, twice as long as either the height or the width of the channels 38.
FIG. 3 illustrates another integrated circuit 100 having an alternative wiring layout configuration. The major difference between integrated circuit 100 and integrated circuit 10 is the configuration of the wiring channels, and hence the configuration of the wiring itself. Wiring channels 138 have a height twice that of the width of the channels 138, and hence the wiring 140 has a greater height than width.
FIG. 4 illustrates another integrated circuit 200 having a plurality of channels 238 into which wiring 240 is deposited. Channels 238 have a height to width ratio of four to one.
FIG. 5 illustrates another integrated circuit 300 having an additional four planes of wiring beneath the four planes of wiring 30, 32, 34, 36. Specifically, beneath the fourth plane of wiring 36 is a fifth plane of wiring 331 which extends in a direction parallel to the first and third planes of wiring 30, 34, namely from the first side surface 16 to the third side surface 20. Beneath the fifth plane of wiring 331 are a sixth plane 333, a seventh plane 335, and an eighth plane 337. The seventh plane of wiring 335 extends from the first side surface 16 to the third side surface 20, while the sixth and eighth planes of wiring 333, 337 extend from the second side surface 18 to the fourth side surface 22. As with the first four planes of wiring 30, 32, 34, 36, the second four planes of wiring 331, 333, 335, 337 are interspersed such that each plane does not extend in the same direction as adjacent planes.
FIG. 6 illustrates another integrated circuit 400 which is similar to integrated circuit 300 (FIG. 5). The difference is that each of the wiring channels 38 in a single plane of wiring is offset relative to the next closest wiring plane extending in the same direction. For example, the wiring channels 38 in the first wiring plane 30 are offset relative to the channels 38 in the third wiring plane 34. Further, the channels 38 in a fifth wiring plane 431 are offset relative to the channels 38 in a seventh wiring plane 435, and channels 38 in a sixth wiring plane 433 are offset relative to those in an eighth wiring plane 437.
The wiring layouts illustrated in FIGS. 1–6 all have capacitive-resistance effects. The capacitive-resistance effect (RC) of the integrated circuit 10 of FIGS. 1–2 can be expressed by the equationRC=2r{acute over (ε)}{acute over (ε)}oL2(4/p2+1/T2),where r equals interconnect resistivity, {acute over (ε)}o equals permittivity of free space, {acute over (ε)} equals the dielectric constant of the insulator material, L is the interconnect length, p is the interconnect pitch, and T is the interconnect thickness. The interconnect resistivity r is a function of the material from which the wire is formed, and cannot be increased as the pitch and/or the thickness of the wire is reduced. It is also assumed that the thickness of the insulator material between the wiring planes is equal to the thickness of the wiring 40, and the width of the wiring 40 is equal to one half the pitch.
Reduction and dissipation of heat caused by current flow in the wiring in an integrated circuit is, as noted, an increasingly important issue. To obtain additional heat conductivity, and thereby remove/reduce heat effects, the wiring can be made thicker. Thicker wires leads, however, to an undesirable increase in capacitance loading and an increase in the total RC.
There exists a need for a multi-level wiring layout, and a method for making the same, which allows for increased heat dissipation while maintaining relatively low capacitive-resistance values.